Acoustic wave device, communication module, and communication apparatus

ABSTRACT

An acoustic wave device of the present application includes a piezoelectric substrate ( 14 ), interdigital transducer electrodes ( 13 ) formed on the piezoelectric substrate ( 14 ), and an SiO 2  film ( 12 ) formed so as to cover the electrodes ( 13 ). The acoustic wave device also includes a displacement adjustment film ( 11 ) formed on the SiO 2  film ( 12 ), and the displacement adjustment film ( 11 ) is formed from a substance whose acoustic velocity is slower than that of the substance forming the SiO 2  film ( 12 ). According to this configuration, it is possible to suppress unnecessary waves as well as improve temperature characteristics. Also, by mounting such an acoustic wave device in a communication module or communication apparatus, it is possible to achieve an improvement in reliability.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of theprior PCT/JP2007/074221, filed on Dec. 17, 2007, the entire contents ofwhich are incorporated herein by reference.

FIELD

The present application relates to an acoustic wave device,communication module, and communication apparatus.

BACKGROUND

There is demand for both a wide band and favorable temperaturecharacteristics to be satisfied in a duplexer and an RF filter used in amobile communication system. Conventionally, a piezoelectric substrateconfigured from 36° to 50° rotated Y-cut X-propagation lithium tantalate(LiTaO₃) has been used in a surface acoustic wave apparatus used in aduplexer or an RF filter. The TCF (Temperature coefficient of frequency)of the piezoelectric substrate has been approximately −40 to −30 ppm/°C. Also, in order to improve the temperature characteristics, there isknown a method of forming a silicon oxide (SiO₂) film having a positiveTCF so as to cover the IDT electrodes on the piezoelectric substrate.

On the other hand, with an object other than improving the TCF, PatentDocument 1 (Japanese Laid-open Patent Publication No. 11-186866)discloses a manufacturing method for a surface acoustic wave apparatusin which an insulating or semiconductive protective film is formed so asto cover the IDT electrodes of the surface acoustic wave apparatus.

Also, Patent Document 2 (Japanese Laid-open Patent Publication No.61-136312) discloses a 1 port surface acoustic wave resonator configuredby forming an electrode made of a metal such as aluminum or gold on apiezoelectric substrate made of crystal or lithium niobate (LiNbO₃),further forming an SiO₂ film, and thereafter planarizing the SiO₂ film.Planarizing the SiO₂ film in this way obtains favorable resonancecharacteristics.

Also, Patent Document 3 (Japanese Patent No. 3885824) discloses aconfiguration including a piezoelectric substrate configured from LiNbO₃having an electrical mechanical coupling coefficient (k²) of 0.025 ormore; at least one electrode that is formed on the piezoelectricsubstrate and is made of a metal whose density is greater than that ofAl, an alloy whose main component is the metal, or a laminated filmconfigured from either a metal whose density is greater than that of Alor an alloy whose main component is the metal, and another metal; afirst insulating layer formed in a region other than a region where theat least one electrode is formed, such that a film thickness of thefirst insulating layer is approximately equal to that of the electrode;and a second insulating layer formed so as to cover the electrode andthe first insulating layer, wherein the density of the electrode is 1.5or more times that of the first insulating layer, the thickness of thesecond insulating layer is in the range of 0.18λ to 0.34λ (where λ isthe wavelength of the surface waves), and the projection height of aconvex portion on the surface of the second insulating layer is 0.03λ orless (where λ is the wavelength of the surface waves). With theconfiguration disclosed in Patent Document 3, the reflection coefficientof the IDT electrodes is sufficiently large, and the deterioration ofcharacteristics due to ripples appearing in resonance characteristicsand the like does not readily occur.

However, the configurations disclosed in the patent documents have thedisadvantage that, as illustrated in FIG. 15, unnecessary waves B appearat a higher frequency than the main response A that is the object in thefrequency response of the absolute value of the admittance (Scoefficient) of the acoustic wave device. The characteristicsillustrated in FIG. 15 are the result of performing a simulation with anFEM (Finite Element Method) using the physical properties illustrated inTable 1 on an acoustic wave device 200 that, as illustrated in FIG. 16,includes IDT electrodes 202 whose period λ is 2 μm on a piezoelectricsubstrate 203, and furthermore includes an SiO₂ film 201 covering theIDT electrodes 202.

TABLE 1 Physical properties that were used Young's Poisson's AcousticSubstance modulus ratio Density Velocity impedance (unit) (GPa) (—)(kg/m³) (m/sec) (Ns/m³) SiO₂ 70.7 0.25 2300 5544 12.8 Au 78.5 0.42 192602019 38.9 SiC 289 0.18 2920 9948 29.0

As illustrated in FIG. 15, if an unnecessary response (unnecessary wavesB) exists, there is the problem that suppression outside the passbanddegrades when a filter is formed using the acoustic wave device.

The relationship between unnecessary wave size and the film thickness ofthe SiO₂ film is illustrated in FIG. 17, and although unnecessary wavescan be suppressed by reducing the film thickness of the SiO₂ film, thereis the problem that, as illustrated in FIG. 18, the temperaturecharacteristics deteriorate if the film thickness of the SiO₂ film isreduced. Note that FIG. 18 illustrates the relationship between the filmthickness of the SiO₂ film and TCF.

SUMMARY

An acoustic wave device of the present application is an acoustic wavedevice provided with a piezoelectric substrate, interdigital transducerelectrodes formed on the piezoelectric substrate, and an insulatinglayer formed so as to cover the electrodes, the acoustic wave deviceincluding: a displacement adjustment film formed on the insulatinglayer, wherein the displacement adjustment film is formed from asubstance whose acoustic velocity is slower than that of a substanceforming the insulating layer.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe appended claims. It is to be understood that both the foregoinggeneral description and the following detailed description are exemplaryand explanatory only and are not restrictive of the invention, asclaimed.

DRAWINGS

FIG. 1 is a cross-sectional diagram of an acoustic wave device accordingto an embodiment.

FIG. 2A is a distribution diagram illustrating an energy distribution ofa resonance frequency when the film thickness of a displacementadjustment film is 1 nm.

FIG. 2B is a distribution diagram illustrating an energy distribution ofan antiresonance frequency when the film thickness of the displacementadjustment film is 1 nm.

FIG. 2C is a distribution diagram illustrating an energy distribution ofunnecessary waves when the film thickness of the displacement adjustmentfilm is 1 nm.

FIG. 3A is a distribution diagram illustrating an energy distribution ofa resonance frequency when the film thickness of the displacementadjustment film is 10 nm.

FIG. 3B is a distribution diagram illustrating an energy distribution ofan antiresonance frequency when the film thickness of the displacementadjustment film is 10 nm.

FIG. 3C is a distribution diagram illustrating an energy distribution ofunnecessary waves when the film thickness of the displacement adjustmentfilm is 10 nm.

FIG. 4A is a distribution diagram illustrating an energy distribution ofa resonance frequency when the film thickness of the displacementadjustment film is 30 nm

FIG. 4B is a distribution diagram illustrating an energy distribution ofan antiresonance frequency when the film thickness of the displacementadjustment film is 30 nm

FIG. 4C is a distribution diagram illustrating an energy distribution ofunnecessary waves when the film thickness of the displacement adjustmentfilm is 30 nm.

FIG. 5 is a characteristics diagram illustrating a relationship betweenthe film thickness of an SiO₂ film and TCF.

FIG. 6 is a characteristics diagram illustrating a relationship betweenthe film thickness of the SiO₂ film and TCF under the conditions of thedisplacement adjustment film illustrated in FIG. 5.

FIG. 7 is a characteristics diagram illustrating a relationship betweenresonance frequency TCF and unnecessary wave levels under the conditionsof the displacement adjustment film illustrated in FIG. 5.

FIG. 8 is a characteristics diagram illustrating a relationship betweenantiresonance frequency TCF and unnecessary wave levels under theconditions of the displacement adjustment film illustrated in FIG. 5.

FIG. 9 is a characteristics diagram illustrating a relationship betweenthe film thickness of the displacement adjustment film and unnecessarywave size in cases in which the displacement adjustment film has beenformed from various substances.

FIG. 10 is a characteristics diagram illustrating a relationship betweenthe acoustic velocity of the displacement adjustment film andunnecessary wave size in cases in which the displacement adjustment filmhas been formed from various substances.

FIG. 11 is a characteristics diagram illustrating a relationship betweenthe film thickness of the displacement adjustment film and unnecessarywave size in cases in which the displacement adjustment film has beenformed from various substances.

FIG. 12A is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 12B is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 12C is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 12D is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 12E is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 12F is a cross-sectional diagram for describing a manufacturingstep for the acoustic wave device of the embodiment.

FIG. 13 is a block diagram illustrating a configuration of acommunication module including the acoustic wave device of theembodiment.

FIG. 14 is a block diagram illustrating a configuration of acommunication apparatus including the acoustic wave device or thecommunication module of the embodiment.

FIG. 15 is a characteristics diagram illustrating frequency responsecharacteristics of a conventional acoustic wave device.

FIG. 16 is a cross-sectional diagram illustrating a configuration of aconventional acoustic wave device.

FIG. 17 is a characteristics diagram illustrating a relationship betweenunnecessary wave size and the film thickness of a SiO₂ film.

FIG. 18 is a characteristics diagram illustrating a relationship betweenthe film thickness of a SiO₂ film and temperature coefficient offrequency.

DESCRIPTION OF THE EMBODIMENT

A first configuration of an acoustic wave device of the presentapplication is an acoustic wave device provided with a piezoelectricsubstrate, interdigital transducer electrodes formed on thepiezoelectric substrate, and an insulating layer formed so as to coverthe electrodes, the acoustic wave device including: a displacementadjustment film formed on the insulating layer, wherein the displacementadjustment film is formed from a substance whose acoustic velocity isslower than that of a substance forming the insulating layer. Accordingto this configuration, it is possible to suppress unnecessary waves aswell as improve temperature characteristics.

The acoustic wave device of the present application can take variousforms such as the following, based on the configuration described above.

Specifically, in the acoustic wave device of the present application, aconfiguration is possible in which the electrodes are configured by ametal, an alloy whose main component is the metal, or a laminated filmconfigured from a metal and another metal.

Also, in the acoustic wave device of the present application, aconfiguration is possible in which the insulating layer is formed fromSiO₂, and the displacement adjustment film is formed from a single layermade of a substance whose acoustic velocity is slower than that of SiO₂,or a laminated film whose main component is any substance from amongsubstances whose acoustic velocity is slower than that of SiO₂.

Also, in the acoustic wave device of the present application, aconfiguration is possible in which the displacement adjustment film isformed from a single layer made of any of Au, Ag, Pt, Ta, Cu, W, Ti, andNi, or a laminated film whose main component is any substance from amongAu, Ag, Pt, Ta, Cu, W, Ti, and Ni.

Also, a second configuration of the acoustic wave device of the presentapplication is an acoustic wave device provided with a piezoelectricsubstrate, interdigital transducer electrodes formed on thepiezoelectric substrate, a first insulating layer formed between theelectrodes and so as to have approximately the same film thickness asthe electrodes, and a second insulating layer formed so as to cover theelectrodes and the first insulating layer, the acoustic wave deviceincluding: a displacement adjustment film formed on the secondinsulating layer, wherein the displacement adjustment film is formedfrom a substance whose acoustic velocity is slower than that of asubstance forming the second insulating layer. According to thisconfiguration, it is possible to suppress unnecessary waves as well asimprove temperature characteristics. Also, since a polishing step isunnecessary in manufacturing, the manufacturing is easy and it ispossible to reduce the manufacturing cost.

Also, a manufacturing method for an acoustic wave device of the presentapplication is a manufacturing method for an acoustic wave deviceprovided with a piezoelectric substrate, interdigital transducerelectrodes formed on the piezoelectric substrate, an insulating layerformed so as to cover the electrodes, and a displacement adjustment filmformed on the insulating layer and configured by a substance whoseacoustic velocity is slower than that of the insulating layer, themanufacturing method including: forming the electrodes on thepiezoelectric substrate; forming the insulating layer on thepiezoelectric substrate so as to cover the electrodes; and forming thedisplacement adjustment film on the insulating layer. According to thismethod, a polishing step is unnecessary in manufacturing, and thereforethe manufacturing is easy and it is possible to reduce the manufacturingcost.

Also, a communication module of the present application includes theacoustic wave device described above.

Also, a communication apparatus of the present application includes thecommunication module described above.

Embodiment 1. Configuration of Acoustic Wave Device

FIG. 1 illustrates a configuration of an acoustic wave device ofEmbodiment 1. In an acoustic wave device 1 in FIG. 1, IDT electrodes 13are formed on a piezoelectric substrate 14, and furthermore an SiO₂ film12 is formed so as to cover the IDT electrodes 13. In the presentembodiment, a displacement adjustment film 11 is furthermore formed onthe SiO₂ film 12. The displacement adjustment film 11 is formed from asingle-layer film made of a substance whose acoustic velocity is slowerthan that of the substance forming the SiO₂ film 12, or a laminated filmwhose main component is a substance whose acoustic velocity is slowerthan that of the substance forming the SiO₂ film 12. For example, it ispreferable that the displacement adjustment film 11 is formed from asingle-layer film made of any of gold (Au), silver (Ag), platinum (Pt),tantalum (Ta), copper (Cu), tungsten (W), titanium (Ti), and nickel(Ni), or a laminated film whose main component is any of the abovesubstances. In particular, Ta and W are preferable since there is littlevariation in the resonance frequency due to Ta and W having an acousticvelocity close to the acoustic velocity of SiO₂. Also, Ti is preferabledue to having excellent adhesion to SiO₂. Note that the SiO₂ film 12 isan example of an insulating layer.

The linear expansion coefficient of a normal substance is positive, andif the acoustic wave device is formed using a common manufacturingmethod, the TCF of the acoustic wave device is negative, and thecharacteristics therefore change if the temperature of the devicechanges. For this reason, SiO₂ having a positive TCF is used incombination in order to bring the TCF close to 0. However, if the filmthickness of the SiO₂ film is increased in order to improve the TCF,there is an increase in the unnecessary wave level as illustrated in thepreviously described FIG. 18. In other words, there is a trade-offrelationship between TCF and unnecessary wave level.

FIG. 2A illustrates an energy distribution of a resonance frequency ofthe main response when the displacement adjustment film 11 is formedfrom Au and has a thickness of 1 nm. FIG. 2B illustrates an energydistribution of an antiresonance frequency in the same configuration.FIG. 2C illustrates an energy distribution of a resonance frequency ofunnecessary waves in the same configuration. FIGS. 3A to 3C illustrateenergy distributions of a resonance frequency of the main response (FIG.3A), an antiresonance frequency (FIG. 3B), and a resonance frequency ofunnecessary waves (FIG. 3C) when the film thickness of the displacementadjustment film 11 is 10 nm. FIGS. 4A to 4C illustrate energydistributions of a resonance frequency of the main response (FIG. 4A),an antiresonance frequency (FIG. 4B), and a resonance frequency ofunnecessary waves (FIG. 4C) when the film thickness of the displacementadjustment film 11 is 30 nm. In each of these figures, a region 21illustrates an energy distribution in the displacement adjustment film11, a region 22 illustrates an energy distribution in the SiO₂ film 12,a region 23 illustrates an energy distribution in the IDT electrodes 13,and a region 24 illustrates an energy distribution in the piezoelectricsubstrate 14.

As illustrated in FIGS. 2A and 2B, if the displacement adjustment film11 is thin, the high-energy regions at the resonance frequency of themain response and the antiresonance frequency reach the vicinity of theinterface between the region 22 of the SiO₂ film 12 and the region 24 ofthe piezoelectric substrate 14, whereas as illustrated in FIGS. 4A and4B, if the displacement adjustment film 11 is thick, the high-energyregions at the resonance frequency of the main response and theantiresonance frequency are concentrated at the surface of the acousticwave device 1 (the region 21 of the displacement adjustment film 11).This is because the acoustic velocity of Au is slower than the acousticvelocity of SiO₂. In contrast, if the displacement adjustment film 11 isformed from a substance whose acoustic velocity is faster than theacoustic velocity of SiO₂, such as silicon carbide (SiC), thehigh-energy regions move to the internal side of the piezoelectricsubstrate 14, the degree of influence of the linear expansioncoefficient of the piezoelectric substrate 14 rises, and the TCFdeteriorates. When the case where Au having a an thickness of 10 nm isformed and the case where SiC having a film thickness of 10 nm is formedare compared as illustrated in FIG. 5, it can be seen that the TCF isimproved when Au is formed. In other words, if the displacementadjustment film 11 is formed from Au, the high-energy regions at theresonance frequency of the main response and the antiresonance frequencyare concentrated at the surface of the acoustic wave device 1, andtherefore the degree of influence of the linear expansion coefficient ofthe piezoelectric substrate 14 falls, and the TCF is improved.

Note that FIG. 5 illustrates the relationship between the film thicknessof the SiO₂ film 12 and TCF in cases in which the displacementadjustment film 11 is formed from Au having a film thickness of 5 nm, Auhaving a film thickness of 10 nm, Au having a film thickness of 20 nm,SiC having a thickness of 10 nm, and in a case in which the displacementadjustment film 11 is not formed (comparison example). In the graphillustrated in FIG. 5, the horizontal axis is the film thickness of theSiO₂ film 12.

However, as illustrated in FIG. 6, if the film thickness of the SiO₂film 12 is set the same and unnecessary wave levels are compared, it canbe seen that the unnecessary wave level rises due to forming thedisplacement adjustment film 11 on the SiO₂ film 12. This is because thehigh-energy regions move to the surface of the acoustic wave device 1,and unnecessary waves are readily generated. Note that FIG. 6illustrates the relationship between the film thickness of the SiO₂ film12 and unnecessary waves under the conditions of the displacementadjustment film 11 illustrated in FIG. 5.

However, as illustrated in FIGS. 7 and 8, if the TCF is set the same anda comparison is performed, it can be seen that there is an improvementwith respect to unnecessary waves since the film thickness of the SiO₂film 12 can be reduced. In the illustrated examples, the closer the TCFis to zero, the better, and therefore a configuration in which Au havinga film thickness of 10 nm is formed is the best. Note that FIG. 7illustrates the relationship between resonance frequency TCF andunnecessary wave levels under the conditions of the displacementadjustment film 11 illustrated in FIG. 5. Also, FIG. 8 illustrates therelationship between antiresonance frequency TCF and unnecessary wavelevels under the conditions of the displacement adjustment film 11illustrated in FIG. 5.

Also, the film thickness of the displacement adjustment film 11 was setto 10 nm, the Young's modulus and density of the displacement adjustmentfilm were changed according to the conditions illustrated in Table 2,and the size of the unnecessary waves was measured in each case. FIGS. 9to 11 illustrate a distribution of the size of the unnecessary waveswhen the resonance frequency TCF was 0 ppm/° C., and it can be seen thatthe slower the acoustic velocity of the substance forming thedisplacement adjustment film 11, the more unnecessary waves aresuppressed. Also, it can be seen that the film thickness of thedisplacement adjustment film 11 has an optimum value.

TABLE 2 Physical properties that were used Young's Poisson's AcousticSubstance modulus ratio Density Velocity impedance (unit) (GPa) (—)(kg/m³) (m/sec) (Ns/m³) SiO₂ TEOS 70.7 0.25 2300 5544 12.8 400 measuredvalue WSST resist 3 0.3 1100 1651 1.8 Au 78.5 0.42 19260 2019 38.9 Cu129.8 0.343 8960 3806 34.1 Ti 120.2 0.321 4500 5168 23.3 Ag 82.7 0.3810490 2808 29.5 Pt 170 0.303 21450 2815 60.4 Ta 185.7 0.33 16600 334555.5 W 411 0.33 19300 4615 89.1 SiC 289 0.18 2920 9948 29.0 Ni 199.50.336 8900 4735

Note that FIGS. 9 and 11 illustrate the relationship between the filmthickness of the displacement adjustment film 11 and unnecessary wavesize in cases in which the displacement adjustment film 11 is formedfrom various substances. FIG. 10 illustrates the relationship betweenthe acoustic velocity of the displacement adjustment film 11 andunnecessary wave size in cases in which the displacement adjustment film11 is formed from various substances. The substances used in themeasurements producing the measurement results illustrated in FIGS. 9and 10 were WSST resist, gold (Au), silver (Ag), platinum (Pt), tantalum(Ta), copper (Cu), tungsten (W), and titanium (Ti). In the measurementsproducing the measurement results illustrated in FIG. 9, measurementswere performed for laminated films including Au and adhesion layers(Ti1, Ti2, and Ti3), in addition to the above substances. Also, thesubstances used in the measurements producing the measurement resultsillustrated in FIG. 11 were Au, Ti, and laminated films including Au andTi. Also, measurements were performed for nickel (Ni) as well, and itwas confirmed that the acoustic velocity was slower than that of SiO₂ asillustrated in Table 2 (not plotted in FIGS. 9 and 11).

As described above, due to forming the displacement adjustment film 11whose acoustic velocity is slower than the acoustic velocity of the SiO₂film 12 on the SiO₂ film 12, energy is concentrated at the surface ofthe acoustic wave device 1. Accordingly, the influence of the linearexpansion coefficient of the piezoelectric substrate 14 decreases, andthe TCF can be improved. Also, the generation of unnecessary waves canbe suppressed since the thickness of the SiO₂ film 12 can be reduced.

Note that although the SiO₂ film 12 is a single-layer film in thepresent embodiment, the same effects can be obtained even if the SiO₂film 12 has a laminated structure including a first insulating layer(e.g., an SiO₂ film) formed so as to have approximately the same filmthickness as the IDT electrodes 13, and a second insulating layer (e.g.,the same SiO₂ film as the first insulating layer) formed so as to coverthe first insulating layer. This configuration eliminates the need for apolishing step in manufacturing, thereby enabling a reduction inmanufacturing cost.

2. Manufacturing Method for Acoustic Wave Device

FIGS. 12A to 12F are cross-sectional diagrams illustrating manufacturingsteps for the acoustic wave device of the present embodiment. Thedisplacement adjustment film 11 used in the manufacturing stepsillustrated in FIGS. 12A to 12F is a laminated film including Au and Ti.

First, the piezoelectric substrate 14 illustrated in FIG. 12A isprepared.

Next, as illustrated in FIG. 12B, a Ti film 13 a that is an adhesionlayer is formed on the surface of the piezoelectric substrate 14, and aCu film 13 b is formed on the Ti film 13 a. Note that in the presentembodiment, the film thickness of the Ti film 13 a is 20 nm, and thefilm thickness of the Cu film 13 b is 100 nm.

Next, as illustrated in FIG. 12C, a photoresist for electrode patterningis formed on the Ti film 13 a and the Cu film 13 b, and patterning isperformed using photolithography. Next, etching processing is performedon the Ti film 13 a and the Cu film 13 b to eliminate the photoresist,thus forming the IDT electrodes 13.

Next, as illustrated in FIG. 12D, the SiO₂ film 12 is formed on thepiezoelectric substrate 11 so as to cover the Ti film 13 a and the Cufilm 13 b. In the present embodiment, the SiO₂ film 12 is formed bycausing growth with use of a CVD method (Chemical Vapor Depositionmethod) until the film thickness reaches 550 nm. Projection portions 12a exist in the formed SiO₂ film 12 at positions over the IDT electrodes12.

Next, as illustrated in FIG. 12E, the surface of the SiO₂ film 12 isplanarized by eliminating the projection portions 12 a of the SiO₂ film12. Note that in the present embodiment, a CMP method (ChemicalMechanical Polishing method) is used for the planarizing processing.

Next, as illustrated in FIG. 12F, a Ti film 11 b that is an adhesionlayer is formed on the surface of the SiO₂ film 12, and an Au film 11 ais grown on the Ti film 11 b by vapor deposition processing, thusforming the displacement adjustment film 11. Note that in the presentembodiment, the film thickness of the Au film 11 a is 15 nm, and thefilm thickness of the Ti film 11 b is 5 nm.

Also, if the film thickness of the SiO₂ film 12 is 0.3 μm or more, theinfluence of the potential of the displacement adjustment film 11 issmall, and therefore no difference in characteristics is seen betweenwhen the displacement adjustment film 11 configured by an Au/Tilaminated film is grounded and floating. Also, even in the case of aconfiguration using Ag, Pt, Ta, Cu, W, Ti, WSST resist, Ni, or the likeinstead of Au, as illustrated in FIG. 9, manufacturing can be performedusing the same manufacturing method as the present embodiment. Also,although a manufacturing method in which the displacement adjustmentfilm 11 configured by an Au/Ti laminated film is described in thepresent embodiment, the same manufacturing method can be used even inthe case of forming a single-layer displacement adjustment film 11.

Note that although the SiO₂ film 12 is a single-layer film in thepresent embodiment, a configuration is possible in which the SiO₂ film12 has a laminated structure including a first insulating layer (e.g.,an SiO₂ film) formed so as to have approximately the same film thicknessas the IDT electrodes 13, and a second insulating layer (e.g., the sameSiO₂ film as the first insulating layer) formed so as to cover the firstinsulating layer. In the manufacturing method in such a case, after theIDT electrodes 13 illustrated in FIG. 12C have been formed, the firstinsulating layer having approximately the same film thickness as the IDTelectrodes 13 is formed between the IDT electrodes 13. At this time, thesurface of the IDT electrodes 13 and the first insulating layer areapproximately planar. Next, the second insulating layer is formed so asto cover the IDT electrodes 13 and the first insulating layer. Byperforming manufacturing in this way, the projection portions 12 a suchas those illustrated in FIG. 12D are not formed, and therefore a stepfor eliminating the projection portions 12 a is not necessary.Accordingly, since polishing work is unnecessary, the manufacturing iseasy and it is possible to reduce the manufacturing cost.

3. Configuration of Communication Module

FIG. 13 illustrates an example of a communication module that includesthe acoustic wave device of the present embodiment. As illustrated inFIG. 13, a duplexer 52 includes a reception filter 54 and a transmissionfilter 55. The reception filter 54 is connected to reception terminals62 a and 62 b that are compatible with, for example, balanced output.Also, the transmission filter 55 is connected to a power amplifier 63.Here, the acoustic wave device 1 of the present embodiment is includedin the reception filter 54 and the transmission filter 55.

In the case of performing a reception operation, the reception filter 54allows, among reception signals input via an antenna terminal 61, onlysignals in a predetermined frequency band to pass, and externallyoutputs such signals via the reception terminals 62 a and 62 b. Also, inthe case of performing a transmission operation, the transmission filter55 allows, among transmission signals input from a transmission terminal64 and amplified by the power amplifier 63, only signals in apredetermined frequency band to pass, and externally outputs suchsignals via the antenna terminal 61.

Note that the configuration of the communication module illustrated inFIG. 13 is an example, and the same effects are obtained even if theacoustic wave device or duplexer of the present embodiment is mounted ina communication module having another form.

4. Configuration of Communication Apparatus

FIG. 14 illustrates an RF block of a mobile phone terminal as an exampleof a communication apparatus including the acoustic wave device of thepresent embodiment. FIG. 14 illustrates a configuration of a mobilephone terminal that is compatible with the GSM (Global System for MobileCommunications) communication system and the W-CDMA (Wideband CodeDivision Multiple Access) communication system. Also, in the presentembodiment, the GSM communication system is compatible with the 850 MHzband, the 950 MHz band, the 1.8 GHz band, and the 1.9 GHz band. Also,although the mobile phone terminal includes a microphone, a speaker, aliquid crystal display, and the like in addition to the configurationillustrated in FIG. 14, such elements are not illustrated in the figuresince they are unnecessary to the description of the present embodiment.Here, the acoustic wave device 1 of the present embodiment is includedin reception filters 54, 76, 77, 78, and 79, and the transmission filter55.

First, an LSI that is targeted for operation is selected by an antennaswitch circuit 72 based on whether the communication system of areception signal input via an antenna 71 is W-CDMA or GSM. If the inputreception signal is compatible with the W-CDMA communication system,switching is performed so that the reception signal is output to theduplexer 52. The reception signal input to the duplexer 52 is limited toa predetermined frequency band by the reception filter 54, and thebalanced reception signal is output to an LNA 73. The LNA 73 amplifiesthe input reception signal, and outputs the amplified signal to an LSI75. In the LSI 75, processing for demodulation to an audio signal isperformed based on the input reception signal, and the operation ofunits in the mobile phone terminal is controlled.

On the other hand, in the case of transmitting a signal, the LSI 75generates a transmission signal. The generated transmission signal isamplified by a power amplifier 74 and input to the transmission filter55. The transmission filter 55 allows, among the input transmissionsignals, only signals in a predetermined frequency band to pass. Thetransmission signals output from the transmission filter 55 are sent tothe antenna switch circuit 72 and then externally output via the antenna71.

Also, if the input reception signal is a signal compatible with the GSMcommunication system, the antenna switch circuit 72 selects one of thereception filters 76 to 79 in accordance with the frequency band, andoutputs the reception signal to the selected reception filter. The bandof the reception signal is limited by the selected one of the receptionfilters 76 to 79, and the resulting signal is input to an LSI 82. TheLSI 82 performs processing for demodulation to an audio signal based onthe input reception signal, and controls the operation of units in themobile phone terminal. On the other hand, in the case of transmitting asignal, the LSI 82 generates a transmission signal. The generatedtransmission signal is amplified by a power amplifier 80 or 81, sent tothe antenna switch circuit 72, and externally output via the antenna 71.

5. Effects of the Embodiment and Other Remarks

According to the present embodiment, by forming, on the SiO₂ film 12,the displacement adjustment film 11 configured from a substance whoseacoustic velocity is slower than that of the substance forming the SiO₂film 12, it is possible to suppress the generation of unnecessary wavesand also improve the TCF. This enables realizing an acoustic wavedevice, a communication module, and a communication apparatus that arehighly reliable.

Note that although a mobile phone terminal, a PHS terminal, and the likeare given as examples of communication apparatuses to which the acousticwave device of the present embodiment or a communication moduleincluding the acoustic wave device of the present embodiment can beapplied, there is no limitation to such communication apparatuses.

The present application is useful to an acoustic wave device such as aSAW (Surface Acoustic Wave) device, which is an example of a device inwhich acoustic waves are applied. Also, the present application isuseful to a communication module and communication device that includesuch an acoustic wave device.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the principlesof the invention and the concepts contributed by the inventor tofurthering the art, and are to be construed as being without limitationto such specifically recited examples and conditions, nor does theorganization of such examples in the specification relate to a showingof the superiority and inferiority of the invention. Although theembodiments of the present inventions have been described in detail, itshould be understood that the various changes, substitutions, andalterations could be made hereto without departing from the sprit andscope of the invention.

1. An acoustic wave device provided with a piezoelectric substrate,interdigital transducer electrodes formed on the piezoelectricsubstrate, and an insulating layer formed so as to cover the electrodes,the acoustic wave device comprising: a displacement adjustment filmformed on the insulating layer, wherein the displacement adjustment filmis formed from a substance whose acoustic velocity is slower than thatof a substance forming the insulating layer.
 2. The acoustic wave deviceaccording to claim 1, wherein the electrodes are configured by a metal,an alloy whose main component is the metal, or a laminated filmconfigured from a metal and another metal.
 3. The acoustic wave deviceaccording to claim 2, wherein the insulating layer is formed from SiO₂,and the displacement adjustment film is formed from a single-layer filmmade of a substance whose acoustic velocity is slower than that of SiO₂,or a laminated film whose main component is any substance from amongsubstances whose acoustic velocity is slower than that of SiO₂.
 4. Theacoustic wave device according to claim 3, wherein the displacementadjustment film is formed from a single-layer film made of any of Au,Ag, Pt, Ta, Cu, W, Ti, and Ni, or a laminated film whose main componentis any substance from among Au, Ag, Pt, Ta, Cu, W, Ti, and Ni.
 5. Anacoustic wave device provided with a piezoelectric substrate,interdigital transducer electrodes formed on the piezoelectricsubstrate, a first insulating layer formed between the electrodes and soas to have approximately the same film thickness as the electrodes, anda second insulating layer formed so as to cover the electrodes and thefirst insulating layer, the acoustic wave device comprising: adisplacement adjustment film formed on the second insulating layer,wherein the displacement adjustment film is formed from a substancewhose acoustic velocity is slower than that of a substance forming thesecond insulating layer.
 6. A manufacturing method for an acoustic wavedevice provided with a piezoelectric substrate, interdigital transducerelectrodes formed on the piezoelectric substrate, an insulating layerformed so as to cover the electrodes, and a displacement adjustment filmformed on the insulating layer and configured by a substance whoseacoustic velocity is slower than that of the insulating layer, themanufacturing method comprising: forming the electrodes on thepiezoelectric substrate; forming the insulating layer on thepiezoelectric substrate so as to cover the electrodes; and forming thedisplacement adjustment film on the insulating layer.
 7. A communicationmodule comprising the acoustic wave device, the acoustic wave devicecomprising: a piezoelectric substrate, interdigital transducerelectrodes formed on the piezoelectric substrate, and an insulatinglayer formed so as to cover the electrodes, and a displacementadjustment film formed on the insulating layer, wherein the displacementadjustment film is formed from a substance whose acoustic velocity isslower than that of a substance forming the insulating layer.
 8. Acommunication apparatus comprising the acoustic wave device, theacoustic wave device comprising: a piezoelectric substrate, interdigitaltransducer electrodes formed on the piezoelectric substrate, and aninsulating layer formed so as to cover the electrodes, and adisplacement adjustment film formed on the insulating layer, wherein thedisplacement adjustment film is formed from a substance whose acousticvelocity is slower than that of a substance forming the insulatinglayer.